In addition to conventional data transmission, modern mobile communication systems provide subscribers with various data transmission features. Mobile communication system services can be generally divided into Teleservices and Bearer Services. A bearer service is a telecommunication service that allows transmission of signals between user-network interfaces. For example, modem services are bearer services. In a teleservice the network also provides terminal equipment services. Speech services, telefax services and videotex services are major teleservices.
One mobile subscriber may typically have a right to various teleservices and network services which are here generally referred to as basic services. The subscriber may have access to a speech, telefax and data service. A mobile-terminating or mobile-originating call can thus require any of these basic services, wherefore the appropriate service should be indicated to the mobile network. For example, in a pan-European mobile communication system GSM, call set-up signalling transmitted by a mobile station contains information on the required basic service in a Bearer Capability Information Element GSM BCIE. The mobile network can thus select the appropriate basic service for mobile-originating calls. Also, ISDN (Integrated Services Data Network) supports this type of signalling: calls from the ISDN to the mobile network contain a similar information element ISDN BCIE that indicates the service required. In that case the subscriber has only one directory number for all services and the services required by the call are identified on the basis of the ISDN BCIE. This is known as Single Numbering Scheme.
Unfortunately the public switched telephone network (PSTN) does not support signalling of service data. Therefore when a call originates from or is routed via the PSTN, the information on the service type of the call will not be transmitted to the mobile station network. In that case, the mobile network should be informed in some other way of the basic service required by the call.
A prior art solution to this problem is a Multinumbering Scheme in which the number of directory numbers of a mobile subscriber is equal to the number of the services to which he/she wishes to receive incoming calls. A directory number is also known as a Mobile Subscriber ISDN Number (MSISDN). A subscriber may have a directory number for a speech service, a telefax service and a modem service, for example. In the multinumbering scheme, a calling subscriber dials one of the directory numbers of the mobile subscriber according to the desired service. In the GSM network, subscriber services are defined in a subscriber's home location register HLR where other subscriber data is also stored permanently. Also, information on the association between the directory numbers and the services of the subscriber is stored in the HLR. Furthermore, a specific BCIE indicating the type of a call and the network resources required for the call is also linked with the directory number (MSIDSN) in the HLR. The BCIE is described e.g. in GSM Recommendation 04.08, version 4.5.0, pp. 423 to 431. The HLR also contains an IMSI (International Mobile Subscriber Identity) used within the GSM system. The mobile subscriber has only one IMSI which is common to all the basic services.
The GSM system also has another subscriber register, a visitor location register VLR, into which some of the subscriber data is copied from the HLR when the subscriber is located within the area of the VLR.
FIG. 2 illustrates a call set-up of a mobile-terminating call in a GSM type of mobile communication system using a multinumbering scheme. In step 1, a call addressed to one of the subscriber's directory numbers arrives at a network gateway mobile switching centre GMSC which sends a routing information inquiry (message 2) to the subscriber's HLR, which is determined by the subscriber's directory number MSISDN. The subscriber's MSISDN number (and possibly ISDN BCIE +HLC+LLC if signalling is supporting the transmission of this data) is also sent along with the routing information inquiry message 2. In connection with a location updating, the information on the VLR in whose area the subscriber is located has been updated to the subscriber's HLR. On the basis of that information, the HLR sends a roaming number request (message 3) to the VLR. In the roaming number request, the mobile subscriber's IMSI and the BCIE (or the ISDN BCIE received in message 2) related to the called MSISDN are sent to the VLR. The BCIE indicates e.g. the network resources required by the call, but not directly the type of the basic service. The VLR will store the received BCIE and allocate a roaming number MSRN (Mobile Station Roaming Number). The VLR will send the allocated roaming number to the HLR in a response message 5. The HLR, in turn, forwards the roaming number to the GMSC that has requested routing information, in a message 6. The routing number space is determined in such a manner that it will route the call every time to the mobile switching centre MSC whose VLR has allocated a roaming number. Thus the GMSC routes the call forwards by sending an initial address message 7 to the mobile switching centre MSC indicated by the roaming number. The MSC makes an inquiry to the VLR, messages 8 and 9, and initiates call set-up which is illustrated with arrows 10 and 11.
In some case there may be between GMSC and MSC different types of transmission links which can be selected for routing. Correspondingly, different services may have different transmission requirements, as a result of which all transmission links are not suitable for all services. In these cases, the GMSC or any intermediate exchange should be able to select the appropriate transmission link.
FIG. 3 illustrates this problem. There is one transmission route from the GMSC to a transit exchange EXC, and there is no need for any selection between the transmission links. There are two transmission routes from the EXC to the MSC: ROUTE.sub.-- 1 and ROUTE.sub.-- 2. Route 2 has transmission devices 31 and 32 that make route 2 unsuitable for some services. For some services, route 2 may, however, be the best alternative because of lower rates, for example. Route 1 may, in turn, have different transmission features. It is also possible that route 1 may handle the same services as route 2, but not vice versa.
When a call originates from a network where signalling supports the transfer of an ISDN BCIE, the GMSC, too, is informed of the service required by the calling subscriber. In that case it can select the appropriate transmission link or forward the information on the service to the transit exchange. But when the call is routed from the PSTN or via the PSTN, the GMSC is not informed of the required service. Then it is not able to select the appropriate transmission link or forward the service data to the GMSC.